I have previously proposed a fixing device made of stainless steel sheet for mounting a sign to a post, the rear of the sign having a channel member with inturned lips, the device comprising a plate to be inserted lengthwise in the channel and a pair of attachment members projecting from opposite ends of the plate through the channel mouth, a strap connected to the attachment members being passed around the post and tightened. This draws the plate against the inside surfaces of the channel lips; the plate providing a substantial bearing area and greatly resisting forcible removal through the channel mouth. It has been found, however, that if the strap is not sufficiently tightened the device can be slid lengthwise out of the channel, and thus the sign can be accidentally or deliberately detached from its mounting.